U.S. Pat. No. 5,511,902 discloses a block that is part of a system for forming a temporary water-retaining structure. The system comprises a plurality of blocks, connecting pins and stakes. The block has an upper surface, a lower surface, four side walls and vertical shafts for accommodating the connecting pins and the stakes. The connecting pins and the corresponding shafts connect the stacked blocks to each other in the vertical direction. The stakes can be inserted by way of a corresponding shaft through the block into a foundation, in order to anchor the block. The block is hollow and can be filled with water through an opening in the upper surface of the block. Said opening is closed by a plug after filling, so that in use the block has a closed top side. The space in the shafts is non-through connected to the space in the water-fillable block.
A disadvantage of U.S. Pat. No. 5,511,902 is that in practice it can take too long for a temporary dam to be constructed. This makes the known system not very suitable for situations in which a temporary water-retaining structure is needed quickly.